The invention relates to a system for monitoring the working of yaw motion dampers in rail vehicles, which rail vehicles are provided with a superstructure which rests on at least two chassis, each provided with one or more wheel axles, in which yaw motions which can arise during running between superstructure and chassis are damped in at least one of the chassis by the said yaw motion dampers which are mounted between the chassis and the superstructure, one on each side of the chassis.
An important factor in assessing the safety and travel-worthiness of rail vehicles, especially rail vehicles which are intended to be used in trains which travel at high speed, is the stability of the rail vehicle. A vehicle can be deemed stable if during running it suffers no (or virtually no) roll or rotation motions, i.e. motions in a direction which does not coincide with the ideal forward motion direction defined by the rail shortly indicated as yaw motions. The stability can be negatively influenced by a variety of factors.
In the first place, owing to the shaping of rail bars and wheel flanges, each vehicle will try by nature to proceed to ride in the middle of the two rail bars. That ideal will seldom, however, be achieved and will only be approached by a self-seeking mode of behaviour. In other words, a rail vehicle will by nature follow a somewhat swaying track. For the purpose of damping the thereby generated roll and rotation motions of the superstructure relative to the chassis, it is known to make use of roll or rotation dampers which are fitted between superstructure and chassis. An example of just such a configuration can be found in DE 19 502 670. In this publication, the damper is adjustable and is controlled by an electronic circuit which receives signals from an acceleration transducer acting in the transverse direction.
It follows from the above that the correct functioning of these roll or rotation dampers is of great importance to maintaining the stability of the vehicle.
At the present moment, it is usual to inspect and/or replace shock absorbers after a certain running time. The running time in question is determined on the basis of historical experience, and in general a certain safety margin will be observed. This implies that in very many cases shock absorbers will be replaced or inspected which are still functioning well and would probably have been able to continue to fulfil their function for a good deal longer. Should the shock absorbers be inspected (which is not always possible), it will in many cases be established following completion of the inspection that the time and cost devoted to the inspection had not in fact been necessary since the shock absorber is continuing to function well.
This problem plays an important role, in particular, in situations in which it is endeavoured to keep the particular vehicle in operation as long as possible without interruptions, such as in the case of rail vehicles, especially rail vehicles which form part of high-speed trains. Such vehicles generally comprise a superstructure which rests, via two bearing systems, on two chassis. Between the superstructure and the chassis there are rotation or roll dampers, which must ensure that the chassis does not suffer the roll motions which may be result from the seeking behaviour of the wheels.
The system described in the above first paragraph, by means of which the sound functioning of a damper can be monitored is described in GB 2 093 946. In this prior art system, the particular sensors comprise a pressure sensor which is installed in the damper and a speed transducer which is also installed in the damper. In addition, an electronic circuit is present, by which the electric signals delivered by the two sensors are processed and compared with each other. If excessively large variances arise, then an indicator is triggered to indicate that the damper is functioning outside its tolerance range.
The sound functioning of such a system is heavily dependent upon the calibration of the electronic circuit by which the signals of the two sensors are processed.
The object of the invention is now to indicate in what way the monitoring of rotation or roll dampers in rail vehicles can be realised such that it is possible reliably to establish when a damper might have to be repaired or replaced.
This object is realized in a system of the sort stated in the introduction which according to the invention is characterized in that the system is further provided with means for comparing the differential signal with a reference value, which means emit a warming signal if the differential signal exceeds the said reference value.
Owing to the fact that the dampers are not monitored individually but are monitored as a group and the measurement signals of the sensors within the group are compared with each other, the underperformance of a damper from the group already quickly becomes apparent.
The output signal of the comparison means can be transferred via cables to a further circuit for processing this signal or can possibly be transported in a wireless manner.
It is preferable in both cases that the system should further be provided with means by which the differential signal is compared with a reference value, which means emit a warning signal if the differential signal exceeds the said reference value.
It is noted that a circuit for processing sensor signals is known per se from U.S. Pat. No. 4,141,236. In this publication, the basis is provided by a damper of the same type as described in the above-named British publication GB-2 093 946. To this is added a circuit by which the signals of both sensors are converted into a possible alarm signal. Here however, it is a matter of sensors which are combined with a single damper.
In a preferred embodiment, the sensor for each damper is formed by at least one force transducer which is connected to the outside of the particular damper, or at least one force transducer which is fitted inside the particular damper, measures being taken to transfer the signal emitted by the sensor to outside the damper.
The said force transducers can at least partly be constructed using strain gauges.
If a change in damper characteristic is not expressed in the damping force but in the associated damper speed, or if the use of force transducers is less desirable for other reasons, then it may be preferable that the sensor for each damper should be formed by at least one pressure transducer which is fitted inside the particular damper, measures being taken to transfer the signal emitted by the sensor to outside the damper.
According to another alternative, the sensor for each damper is formed by an acceleration transducer acting in the longitudinal direction, which is fastened to the chassis in the vicinity of the particular damper.
In a further developed embodiment, in respect of each damper an acceleration transducer in the longitudinal direction of the damper is fastened to the chassis, which acceleration transducer emits an output signal to a series circuit of an amplifier and an integrator, for each damper the output signal of the working-pressure sensor or damping-force sensor being divided in a divider circuit by the integrated output signal of the acceleration transducer in the longitudinal direction of the damper and the resultant quotients being compared with each other in the comparator.
Although the above-mentioned embodiments can be realised totally by means of analogue electronics, it is especially preferable, owing to the low frequencies of the roll motions and the consequentially long averaging periods, to use digital methods. The use of very large, accurate and hence expensive capacitors, for example, can thereby be avoided.
It is therefore preferable that the two circuits for determining an effective value of the filter output signal and the comparator should be realised as digital circuits and as a programmed processor respectively and that an analogue/digital converter is included after each band filter.
It is also preferable that the two band filters, the two circuits for determining an effective value of the filter output signal and the comparator are realised as digital circuits and as a programmed processor respectively and that an analogue/digital converter is included after each amplifier.
It is further preferable that the integrators, the divider circuits and the comparator are realised as digital circuits and as a programmed processor respectively and that the amplifiers for amplifying the signal of the acceleration transducers in the longitudinal direction of the dampers are followed by an A/D converter.
To enable the digital filters in the abovenamed embodiment to be accurately adjusted and possibly fine-tuned during operation, it is preferable that the chassis is provided with an acceleration transducer which is fastened such that the acceleration of the chassis in the transverse direction is measured, and that the output signal of the acceleration transducer is fed to the series circuit of an amplifier, an analogue/digital converter and a digital spectrum analyser by which the band width of the central roll frequency is determined, and that the digital filters are readjusted on the basis of the determined band width.